Group B streptococci (GBS; Streptococcus agalactiae), although generally carried asymptomatically, can cause invasive disease in newborns, pregnant women, and immunocompromised adults. Group B streptococcus is the most common cause of neonatal and obstetric sepsis and an increasingly important cause of septicaemia in the elderly and immunocompromised patients. The incidence of neonatal GBS sepsis has been reduced in recent years by the use of intrapartum antibiotic prophylaxis, but there are many problems with this approach.
Knowledge of the distribution of GBS types (including capsular polysaccharide gene serotypes, serosubtypes; protein antigen gene subtypes; and mobile genetic element subtypes) is needed to determine the optimal formulation of vaccine antigens and in diagnostic and research applications. Type distribution based on one geographic location or small numbers of patients may not be generally applicable. Continued monitoring will be necessary to assess the prevalence of different GBS types.
Nine capsular polysaccharide GBS serotypes have been described (Harrison et al., 1998J. Infect. Disease 177:998; Hickman et al., 1999 Pediatrics 104:203). Various serotyping methods have been used, including immuno-precipitation (Wilkinson and Moody, 1969 J. Bacteriol. 97:629), enzyme immunoassay (Holm and Hakansson, 1988 J. Immunol. Methods 106:89), coagglutination (Hakansson et al., 1992 J. Clin. Microbiol. 30:3268), counter-immunoelectrophoresis, and capillary precipitation (Triscott and Davies, 1979 Aust. J. Expt. Biol. Med. Sci. 57:521), latex agglutination (Zuerlein et al., 1991), fluorescence microscopy (Cropp et al., 1974) and inhibition-ELISA (Arakere et al., 1999 J. Clin. Microbiol. 37:2564). These methods are labour-intensive and require high-titered serotype-specific antisera, which are expensive and difficult to make and commercially available for only six serotypes—Ia to V (Arakere et al., 1999, supra). Molecular genotyping methods, such as pulsed-field gel electrophoresis (Rolland et al., 1999J. Clin. Microbiol. 37:1892), restriction endonuclease analysis (Nagano et al., 1991 J. Medical Microbiol. 35:297) are useful for epidemiological studies but do not generally identify serotypes. Consequently, there is a need for a reliable molecular method for GBS serotype identification.